The objectives of this proposal are to devise and perfect protocols for purifying and characterizing the human hematopoietic stem cell, as well as multipotent and committed progenitors. We have successfully applied the general principles which were used in the laboratory of Dr. Irving L. Weissman at Stanford University for the purification of the mouse stem cell. We have developed the necessary in vitro and in vivo systems which have allowed us to analyze the differentiation potential of human stem cells. In addition, we have devised a means of purifying human stem cells based on their cell surface and mitochondrial staining characteristics. By combining our cell purification scheme and our unique assay systems we have purified the human stem cell to near homogeneity. Over the years 05-08 of this grant we will use the assays we have developed to identify and characterize human stem cell subsets, and to characterize normal and aberrant stem cell development. We will analyze stem cells isolated from patients with leukemia and lymphoma in order to determine the degree of stem cell involvement by the disease processes. In particular, we will analyze stem cell preparations for chromosomal translocations indicative of the underlying disease (see Project III). Further, we will begin a clinical trial which will analyze the utility of human stem cells for bone marrow transplantation (see Projects I and II).